Adding Payed Subscriptions, User Login and Download Limter to Current Site

Greetings Coders! I currently have a website offering free downloads and I want this to change to be on a paid, monthly subscription basis. I have everything completed on my site, so there's no need to change much, I would like the new system to do the following: -Monthly payment subscription integrated with paypal. -A Bandwith Limiter, with user stats displayed (for example, free users have 3GB of transfer a month, payed users have Unlimited, and for the users stats i would like it to display to free users 'you have download 2/5GB this month' etc -User access to be upgraded automatically once payment is received and thats pretty much it! Looking forward to working with you and answering any questions you may have! Kind Regards, James